From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 04C8C2376FC for ; Tue, 5 Aug 2025 10:47:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754390822; cv=none; b=ZlbuGWlfPIVohSmqR7hTGZXUKbdSmoT8itDIl53/IJe1OqELw6159aAMnp7wIPalw2wdhb3kjQxqMXDY1kFwaLojL3MnfQdPYNVqmM/rgVNrLzKw/qZfCKEuQYaU6gfkx4N0ky2EAUcO9z+0oXwNRDiaaFsioMxr16DQDzPs148= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1754390822; c=relaxed/simple; bh=VBp86IUrGuile9rvR/+BhRH8QefDTYlkuOL6DfbX7hY=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=ZpljyyEQ0O0hxoeQ+gpvW5t9J2JwibsoZUg4044rBf0cvizlet3X8TAD3AaBeJXlQDV06s2nNM2Xos57yY4h3fsidta8S4CG/l60kU0TUJ8ZT2YOdRd3hfhALoZ53EdjgC05IfHMQSP2EipBojpiNtUhtuDyEabf+VZjt/DYnxI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=IYjqzzL4; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="IYjqzzL4" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1754390820; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=wk5GXKT9wz3dvDgQdeYLI9qgkV6XRvZlyWZQe8HtFwg=; b=IYjqzzL4e3GxfKT4ospdpllArqQwSYk2Y5d0Ch8ZGz65BBxSw1Vy6fmXFi8pmPr/vs1Vdm hjxBRKPDNUgVOt+t7vatshaaIPMPN6x7KnnEIfPlLaLub4cYVO2wkWxo8/97NURO2ZTlcb jkCrzvqxXx0DFfC2G/J1bTdgITLWKHU= Received: from mail-lf1-f71.google.com (mail-lf1-f71.google.com [209.85.167.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-589-pgTEygjpOMqyfpN6HQ0f2Q-1; Tue, 05 Aug 2025 06:46:58 -0400 X-MC-Unique: pgTEygjpOMqyfpN6HQ0f2Q-1 X-Mimecast-MFC-AGG-ID: pgTEygjpOMqyfpN6HQ0f2Q_1754390817 Received: by mail-lf1-f71.google.com with SMTP id 2adb3069b0e04-55b8422dbdaso2883379e87.0 for ; Tue, 05 Aug 2025 03:46:58 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1754390817; x=1754995617; h=content-transfer-encoding:in-reply-to:from:content-language :references:cc:to:subject:user-agent:mime-version:date:message-id :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=wk5GXKT9wz3dvDgQdeYLI9qgkV6XRvZlyWZQe8HtFwg=; b=TUVHc9xrknwzyjnuKEe6249s6i5sPyGV90hWOlTo9EhxtdjZryMqKUSaUtxvltq04P MLbFRw0UNCSnjUhuywy+7jiqGYUnZ8xMhh6viomcBJb8PML+OI0kT2sik4v8GNyHRxcD stNuUu79uKdayuJsmVOPlwyJ5i4jS8sLWHFmgk55+1HlF/bCNnfbs7piRPx6ZgtUG3fS uKEeBeWGyhX37ON/lNMOig2fdMUUombaZTwuOdh2u/izvnIjJsnO9hepkCels4wXlk5z GkcqvIo9M0q+xCAdTFxy1wiO3EGYoM/dhF7MH57D0mv2UDeCCGVDlXRphtHIVmCLhUIr SmfQ== X-Forwarded-Encrypted: i=1; AJvYcCU4HV7UEl+auTRYo21GVicy5g2kIc/R6p/uUzFjqiZN656ii+evOPMKGbczf6LmLrP1Q85O6Q0iPpiQ1J4=@vger.kernel.org X-Gm-Message-State: AOJu0YzIELEvTRltoPQf+kXJHnIQBZTU/RcbhVjQNUeGoat9/vSKSg2c o3cihnqjXCmjYUq3wg5wINYhP+p4SOCzvnBjQNScF2if4etLbEPyBoIpfQi9IAuA/YGWjBH7na0 4U+N0LVzAHIh9lT+7KqHEibBVsSYf3GfBh2Gk/IbSEw+YaSQya/yIkxBk4MB8tvM8 X-Gm-Gg: ASbGncseOlTTfy2ZC76q/yEpoBRhoekv1p9OknXra/UzGEYWsVVp/BsyX+sl91xfuSM DW227zZ7hLbBt9yOYZGssaq9mh3Pmoqjy0aEUQWwYb5mAYx0Yjxjasd5BYkQ6wUoglZfVmt4wdI Bs/cto9wOsqSaQPPe/ShI8/35Haoutj0Y8y+wo4shJyeHS7yy/evX2tnTHH5TE2sevSkV2xelat QcaASeO/maDvSbjLTGZuRX9o7HN2yl317LwcRGYPD2rxdoU6eHLROvizDTJy9hQcGxW+q/rAIWv am7G7iDcLE8jJzyFfBNyll4/JgJ0m9spn+w1ZB6fHhk7kjNyaccxVABrs5gfkM22AA== X-Received: by 2002:a05:6512:3b07:b0:55b:958f:8c2f with SMTP id 2adb3069b0e04-55b97b9f381mr4069008e87.49.1754390816960; Tue, 05 Aug 2025 03:46:56 -0700 (PDT) X-Google-Smtp-Source: AGHT+IHd9Bp5Ekm55BL1kqJkB8HhmkPyDmXgdV3CuPhFjBM5LjSOKm7EIc8UH12gC8OvPnbsri0MZA== X-Received: by 2002:a05:6512:3b07:b0:55b:958f:8c2f with SMTP id 2adb3069b0e04-55b97b9f381mr4068990e87.49.1754390816427; Tue, 05 Aug 2025 03:46:56 -0700 (PDT) Received: from [192.168.1.86] (85-23-48-6.bb.dnainternet.fi. [85.23.48.6]) by smtp.gmail.com with ESMTPSA id 2adb3069b0e04-55b88c99041sm1928200e87.81.2025.08.05.03.46.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 05 Aug 2025 03:46:55 -0700 (PDT) Message-ID: Date: Tue, 5 Aug 2025 13:46:55 +0300 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [v2 02/11] mm/thp: zone_device awareness in THP handling code To: Balbir Singh , Zi Yan Cc: David Hildenbrand , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Karol Herbst , Lyude Paul , Danilo Krummrich , David Airlie , Simona Vetter , =?UTF-8?B?SsOpcsO0bWUgR2xpc3Nl?= , Shuah Khan , Barry Song , Baolin Wang , Ryan Roberts , Matthew Wilcox , Peter Xu , Kefeng Wang , Jane Chu , Alistair Popple , Donet Tom , Matthew Brost , Francois Dugast , Ralph Campbell References: <20250730092139.3890844-1-balbirs@nvidia.com> <14aeaecc-c394-41bf-ae30-24537eb299d9@nvidia.com> <71c736e9-eb77-4e8e-bd6a-965a1bbcbaa8@nvidia.com> <47BC6D8B-7A78-4F2F-9D16-07D6C88C3661@nvidia.com> <2406521e-f5be-474e-b653-e5ad38a1d7de@redhat.com> <920a4f98-a925-4bd6-ad2e-ae842f2f3d94@redhat.com> <196f11f8-1661-40d2-b6b7-64958efd8b3b@redhat.com> <087e40e6-3b3f-4a02-8270-7e6cfdb56a04@redhat.com> <6a08fa8f-bc39-4389-aa52-d95f82538a91@redhat.com> <6442f975-6363-4969-a0bf-55d06eec9528@nvidia.com> Content-Language: en-US From: =?UTF-8?Q?Mika_Penttil=C3=A4?= In-Reply-To: <6442f975-6363-4969-a0bf-55d06eec9528@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 8/5/25 13:36, Balbir Singh wrote: > On 8/5/25 20:35, Mika Penttilä wrote: >> On 8/5/25 13:27, Balbir Singh wrote: >> >>> On 8/5/25 14:24, Mika Penttilä wrote: >>>> Hi, >>>> >>>> On 8/5/25 07:10, Balbir Singh wrote: >>>>> On 8/5/25 09:26, Mika Penttilä wrote: >>>>>> Hi, >>>>>> >>>>>> On 8/5/25 01:46, Balbir Singh wrote: >>>>>>> On 8/2/25 22:13, Mika Penttilä wrote: >>>>>>>> Hi, >>>>>>>> >>>>>>>> On 8/2/25 13:37, Balbir Singh wrote: >>>>>>>>> FYI: >>>>>>>>> >>>>>>>>> I have the following patch on top of my series that seems to make it work >>>>>>>>> without requiring the helper to split device private folios >>>>>>>>> >>>>>>>> I think this looks much better! >>>>>>>> >>>>>>> Thanks! >>>>>>> >>>>>>>>> Signed-off-by: Balbir Singh >>>>>>>>> --- >>>>>>>>> include/linux/huge_mm.h | 1 - >>>>>>>>> lib/test_hmm.c | 11 +++++- >>>>>>>>> mm/huge_memory.c | 76 ++++------------------------------------- >>>>>>>>> mm/migrate_device.c | 51 +++++++++++++++++++++++++++ >>>>>>>>> 4 files changed, 67 insertions(+), 72 deletions(-) >>>>>>>>> >>>>>>>>> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h >>>>>>>>> index 19e7e3b7c2b7..52d8b435950b 100644 >>>>>>>>> --- a/include/linux/huge_mm.h >>>>>>>>> +++ b/include/linux/huge_mm.h >>>>>>>>> @@ -343,7 +343,6 @@ unsigned long thp_get_unmapped_area_vmflags(struct file *filp, unsigned long add >>>>>>>>> vm_flags_t vm_flags); >>>>>>>>> >>>>>>>>> bool can_split_folio(struct folio *folio, int caller_pins, int *pextra_pins); >>>>>>>>> -int split_device_private_folio(struct folio *folio); >>>>>>>>> int __split_huge_page_to_list_to_order(struct page *page, struct list_head *list, >>>>>>>>> unsigned int new_order, bool unmapped); >>>>>>>>> int min_order_for_split(struct folio *folio); >>>>>>>>> diff --git a/lib/test_hmm.c b/lib/test_hmm.c >>>>>>>>> index 341ae2af44ec..444477785882 100644 >>>>>>>>> --- a/lib/test_hmm.c >>>>>>>>> +++ b/lib/test_hmm.c >>>>>>>>> @@ -1625,13 +1625,22 @@ static vm_fault_t dmirror_devmem_fault(struct vm_fault *vmf) >>>>>>>>> * the mirror but here we use it to hold the page for the simulated >>>>>>>>> * device memory and that page holds the pointer to the mirror. >>>>>>>>> */ >>>>>>>>> - rpage = vmf->page->zone_device_data; >>>>>>>>> + rpage = folio_page(page_folio(vmf->page), 0)->zone_device_data; >>>>>>>>> dmirror = rpage->zone_device_data; >>>>>>>>> >>>>>>>>> /* FIXME demonstrate how we can adjust migrate range */ >>>>>>>>> order = folio_order(page_folio(vmf->page)); >>>>>>>>> nr = 1 << order; >>>>>>>>> >>>>>>>>> + /* >>>>>>>>> + * When folios are partially mapped, we can't rely on the folio >>>>>>>>> + * order of vmf->page as the folio might not be fully split yet >>>>>>>>> + */ >>>>>>>>> + if (vmf->pte) { >>>>>>>>> + order = 0; >>>>>>>>> + nr = 1; >>>>>>>>> + } >>>>>>>>> + >>>>>>>>> /* >>>>>>>>> * Consider a per-cpu cache of src and dst pfns, but with >>>>>>>>> * large number of cpus that might not scale well. >>>>>>>>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c >>>>>>>>> index 1fc1efa219c8..863393dec1f1 100644 >>>>>>>>> --- a/mm/huge_memory.c >>>>>>>>> +++ b/mm/huge_memory.c >>>>>>>>> @@ -72,10 +72,6 @@ static unsigned long deferred_split_count(struct shrinker *shrink, >>>>>>>>> struct shrink_control *sc); >>>>>>>>> static unsigned long deferred_split_scan(struct shrinker *shrink, >>>>>>>>> struct shrink_control *sc); >>>>>>>>> -static int __split_unmapped_folio(struct folio *folio, int new_order, >>>>>>>>> - struct page *split_at, struct xa_state *xas, >>>>>>>>> - struct address_space *mapping, bool uniform_split); >>>>>>>>> - >>>>>>>>> static bool split_underused_thp = true; >>>>>>>>> >>>>>>>>> static atomic_t huge_zero_refcount; >>>>>>>>> @@ -2924,51 +2920,6 @@ static void __split_huge_zero_page_pmd(struct vm_area_struct *vma, >>>>>>>>> pmd_populate(mm, pmd, pgtable); >>>>>>>>> } >>>>>>>>> >>>>>>>>> -/** >>>>>>>>> - * split_huge_device_private_folio - split a huge device private folio into >>>>>>>>> - * smaller pages (of order 0), currently used by migrate_device logic to >>>>>>>>> - * split folios for pages that are partially mapped >>>>>>>>> - * >>>>>>>>> - * @folio: the folio to split >>>>>>>>> - * >>>>>>>>> - * The caller has to hold the folio_lock and a reference via folio_get >>>>>>>>> - */ >>>>>>>>> -int split_device_private_folio(struct folio *folio) >>>>>>>>> -{ >>>>>>>>> - struct folio *end_folio = folio_next(folio); >>>>>>>>> - struct folio *new_folio; >>>>>>>>> - int ret = 0; >>>>>>>>> - >>>>>>>>> - /* >>>>>>>>> - * Split the folio now. In the case of device >>>>>>>>> - * private pages, this path is executed when >>>>>>>>> - * the pmd is split and since freeze is not true >>>>>>>>> - * it is likely the folio will be deferred_split. >>>>>>>>> - * >>>>>>>>> - * With device private pages, deferred splits of >>>>>>>>> - * folios should be handled here to prevent partial >>>>>>>>> - * unmaps from causing issues later on in migration >>>>>>>>> - * and fault handling flows. >>>>>>>>> - */ >>>>>>>>> - folio_ref_freeze(folio, 1 + folio_expected_ref_count(folio)); >>>>>>>>> - ret = __split_unmapped_folio(folio, 0, &folio->page, NULL, NULL, true); >>>>>>>>> - VM_WARN_ON(ret); >>>>>>>>> - for (new_folio = folio_next(folio); new_folio != end_folio; >>>>>>>>> - new_folio = folio_next(new_folio)) { >>>>>>>>> - zone_device_private_split_cb(folio, new_folio); >>>>>>>>> - folio_ref_unfreeze(new_folio, 1 + folio_expected_ref_count( >>>>>>>>> - new_folio)); >>>>>>>>> - } >>>>>>>>> - >>>>>>>>> - /* >>>>>>>>> - * Mark the end of the folio split for device private THP >>>>>>>>> - * split >>>>>>>>> - */ >>>>>>>>> - zone_device_private_split_cb(folio, NULL); >>>>>>>>> - folio_ref_unfreeze(folio, 1 + folio_expected_ref_count(folio)); >>>>>>>>> - return ret; >>>>>>>>> -} >>>>>>>>> - >>>>>>>>> static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, >>>>>>>>> unsigned long haddr, bool freeze) >>>>>>>>> { >>>>>>>>> @@ -3064,30 +3015,15 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd, >>>>>>>>> freeze = false; >>>>>>>>> if (!freeze) { >>>>>>>>> rmap_t rmap_flags = RMAP_NONE; >>>>>>>>> - unsigned long addr = haddr; >>>>>>>>> - struct folio *new_folio; >>>>>>>>> - struct folio *end_folio = folio_next(folio); >>>>>>>>> >>>>>>>>> if (anon_exclusive) >>>>>>>>> rmap_flags |= RMAP_EXCLUSIVE; >>>>>>>>> >>>>>>>>> - folio_lock(folio); >>>>>>>>> - folio_get(folio); >>>>>>>>> - >>>>>>>>> - split_device_private_folio(folio); >>>>>>>>> - >>>>>>>>> - for (new_folio = folio_next(folio); >>>>>>>>> - new_folio != end_folio; >>>>>>>>> - new_folio = folio_next(new_folio)) { >>>>>>>>> - addr += PAGE_SIZE; >>>>>>>>> - folio_unlock(new_folio); >>>>>>>>> - folio_add_anon_rmap_ptes(new_folio, >>>>>>>>> - &new_folio->page, 1, >>>>>>>>> - vma, addr, rmap_flags); >>>>>>>>> - } >>>>>>>>> - folio_unlock(folio); >>>>>>>>> - folio_add_anon_rmap_ptes(folio, &folio->page, >>>>>>>>> - 1, vma, haddr, rmap_flags); >>>>>>>>> + folio_ref_add(folio, HPAGE_PMD_NR - 1); >>>>>>>>> + if (anon_exclusive) >>>>>>>>> + rmap_flags |= RMAP_EXCLUSIVE; >>>>>>>>> + folio_add_anon_rmap_ptes(folio, page, HPAGE_PMD_NR, >>>>>>>>> + vma, haddr, rmap_flags); >>>>>>>>> } >>>>>>>>> } >>>>>>>>> >>>>>>>>> @@ -4065,7 +4001,7 @@ static int __folio_split(struct folio *folio, unsigned int new_order, >>>>>>>>> if (nr_shmem_dropped) >>>>>>>>> shmem_uncharge(mapping->host, nr_shmem_dropped); >>>>>>>>> >>>>>>>>> - if (!ret && is_anon) >>>>>>>>> + if (!ret && is_anon && !folio_is_device_private(folio)) >>>>>>>>> remap_flags = RMP_USE_SHARED_ZEROPAGE; >>>>>>>>> >>>>>>>>> remap_page(folio, 1 << order, remap_flags); >>>>>>>>> diff --git a/mm/migrate_device.c b/mm/migrate_device.c >>>>>>>>> index 49962ea19109..4264c0290d08 100644 >>>>>>>>> --- a/mm/migrate_device.c >>>>>>>>> +++ b/mm/migrate_device.c >>>>>>>>> @@ -248,6 +248,8 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, >>>>>>>>> * page table entry. Other special swap entries are not >>>>>>>>> * migratable, and we ignore regular swapped page. >>>>>>>>> */ >>>>>>>>> + struct folio *folio; >>>>>>>>> + >>>>>>>>> entry = pte_to_swp_entry(pte); >>>>>>>>> if (!is_device_private_entry(entry)) >>>>>>>>> goto next; >>>>>>>>> @@ -259,6 +261,55 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, >>>>>>>>> pgmap->owner != migrate->pgmap_owner) >>>>>>>>> goto next; >>>>>>>>> >>>>>>>>> + folio = page_folio(page); >>>>>>>>> + if (folio_test_large(folio)) { >>>>>>>>> + struct folio *new_folio; >>>>>>>>> + struct folio *new_fault_folio; >>>>>>>>> + >>>>>>>>> + /* >>>>>>>>> + * The reason for finding pmd present with a >>>>>>>>> + * device private pte and a large folio for the >>>>>>>>> + * pte is partial unmaps. Split the folio now >>>>>>>>> + * for the migration to be handled correctly >>>>>>>>> + */ >>>>>>>>> + pte_unmap_unlock(ptep, ptl); >>>>>>>>> + >>>>>>>>> + folio_get(folio); >>>>>>>>> + if (folio != fault_folio) >>>>>>>>> + folio_lock(folio); >>>>>>>>> + if (split_folio(folio)) { >>>>>>>>> + if (folio != fault_folio) >>>>>>>>> + folio_unlock(folio); >>>>>>>>> + ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl); >>>>>>>>> + goto next; >>>>>>>>> + } >>>>>>>>> + >>>>>>>> The nouveau migrate_to_ram handler needs adjustment also if split happens. >>>>>>>> >>>>>>> test_hmm needs adjustment because of the way the backup folios are setup. >>>>>> nouveau should check the folio order after the possible split happens. >>>>>> >>>>> You mean the folio_split callback? >>>> no, nouveau_dmem_migrate_to_ram(): >>>> .. >>>> sfolio = page_folio(vmf->page); >>>> order = folio_order(sfolio); >>>> ... >>>> migrate_vma_setup() >>>> .. >>>> if sfolio is split order still reflects the pre-split order >>>> >>> Will fix, good catch! >>> >>>>>>>>> + /* >>>>>>>>> + * After the split, get back the extra reference >>>>>>>>> + * on the fault_page, this reference is checked during >>>>>>>>> + * folio_migrate_mapping() >>>>>>>>> + */ >>>>>>>>> + if (migrate->fault_page) { >>>>>>>>> + new_fault_folio = page_folio(migrate->fault_page); >>>>>>>>> + folio_get(new_fault_folio); >>>>>>>>> + } >>>>>>>>> + >>>>>>>>> + new_folio = page_folio(page); >>>>>>>>> + pfn = page_to_pfn(page); >>>>>>>>> + >>>>>>>>> + /* >>>>>>>>> + * Ensure the lock is held on the correct >>>>>>>>> + * folio after the split >>>>>>>>> + */ >>>>>>>>> + if (folio != new_folio) { >>>>>>>>> + folio_unlock(folio); >>>>>>>>> + folio_lock(new_folio); >>>>>>>>> + } >>>>>>>> Maybe careful not to unlock fault_page ? >>>>>>>> >>>>>>> split_page will unlock everything but the original folio, the code takes the lock >>>>>>> on the folio corresponding to the new folio >>>>>> I mean do_swap_page() unlocks folio of fault_page and expects it to remain locked. >>>>>> >>>>> Not sure I follow what you're trying to elaborate on here >>>> do_swap_page: >>>> .. >>>> if (trylock_page(vmf->page)) { >>>> ret = pgmap->ops->migrate_to_ram(vmf); >>>> <- vmf->page should be locked here even after split >>>> unlock_page(vmf->page); >>>> >>> Yep, the split will unlock all tail folios, leaving the just head folio locked >>> and this the change, the lock we need to hold is the folio lock associated with >>> fault_page, pte entry and not unlock when the cause is a fault. The code seems >>> to do the right thing there, let me double check >> Yes the fault case is ok. But if migrate not for a fault, we should not leave any page locked >> > migrate_vma_finalize() handles this But we are in migrate_vma_collect_pmd() after the split, and try to collect the pte, locking the page again. So needs to be unlocked after the split. > > Balbir >